Because inductors ‘prevent’ current from changing rapidly, it behaves like a ‘resistor’ under changing current (i.e. You can read the Wikipage to find out how reactance is calculated, but basically it has to do with the frequency of the input voltage, and the inductance of the coil. When operated on AC power, the inductance produces significant reactance which cannot be ignored. Because the solenoid is made of a coil, it not only has coil resistance but also inductance. The catch is exactly in the fact that sprinkler solenoids are powered by AC voltage. In fact, my sprinkler transformer is only rated 750 mA output current, so it can’t provide enough current to drive even one solenoid?! If you think about it for a while, you might realize something is not quite right here: if we apply 24V on the solenoid, wouldn’t that produce a 24 V / 24.1 ohm = 1 amp current draw? That’s quite steep. According to the multimeter, one measures 32.3 ohm, and the other measures 24.1 ohm. I have two example solenoids, one made by Orbit and one made by Hunter. Let’s start by measuring the resistance of the sprinkler solenoid. This also means if your water pressure is too low you may not be able to completely stop the water flow. Because closing the valve relies on internal pressure build-up, it usually takes a few seconds to completely stop the water flow. This allows the water pressure to build up internally hence stopping the flow. Removing the voltage causes the rod to revert back to its original position. This releases the internal water pressure thus opening the valve, allowing water to flow through the valve. Applying 24VAC on the two wires energizes the coil, and causes the rod to contract into the solenoid. The solenoid has two wires connected to its internal coil. At the center of the solenoid is a rod supported by a spring. The electric part of a sprinkler valve is the solenoid - it’s a cylindrical-shaped thing screwed into the valve. That’s why if you look at a standard sprinkler transformer, the output is usually AC. While most valves indeed CAN be powered by DC voltage (see below), they are designed to work with AC voltage in the range of 22VAC to 28VAC. It’s a common mistake to assume sprinkler valves work with DC voltage. If you are designing a sprinkler controller circuit, understanding these properties can be helpful. I often get questions about sprinkler valves, so in this post I will explain the basic electric properties of sprinkler valves. Note: check out our OpenSprinkler DC-powered version, which uses an innovative circuit design that drives sprinkler solenoids using DC-only voltage.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |